[TD]oblique section lines

src/Mod/TechDraw/App/DrawUtil.cpp

@@ -284,6 +284,62 @@ bool DrawUtil::fpCompare(const double& d1, const double& d2, double tolerance)
     return result;
 }
 
+//brute force intersection points of line(point, dir) with box(xRange, yRange)
+std::pair<Base::Vector3d, Base::Vector3d> DrawUtil::boxIntersect2d(Base::Vector3d point,
+                                                                   Base::Vector3d dirIn,
+                                                                   double xRange,
+                                                                   double yRange) 
+{
+    std::pair<Base::Vector3d, Base::Vector3d> result;
+    Base::Vector3d p1, p2;
+    Base::Vector3d dir = dirIn;
+    dir.Normalize();
+    // y = mx + b
+    // m = (y1 - y0) / (x1 - x0)
+    if (DrawUtil::fpCompare(dir.x, 0.0) ) {
+        p1 = Base::Vector3d(0.0, - yRange / 2.0, 0.0);  
+        p2 = Base::Vector3d(0.0, yRange / 2.0, 0.0);
+    } else {
+        double slope = dir.y / dir.x;
+        double left = -xRange / 2.0;
+        double right = xRange / 2.0;
+        double top = yRange / 2.0;
+        double bottom = -yRange / 2.0;
+        double yLeft   = point.y - slope * (point.x - left) ;
+        double yRight  = point.y - slope * (point.x - right);
+        double xTop    = point.x - ( (point.y - top) / slope );
+        double xBottom = point.x - ( (point.y - bottom) / slope );
+
+        if ( (bottom < yLeft) &&
+             (top > yLeft) )  {
+            p1 = Base::Vector3d(left, yLeft);
+        } else if (yLeft <= bottom) {
+            p1 = Base::Vector3d(xBottom, bottom);
+        } else if (yLeft >= top) {
+            p1 = Base::Vector3d(xTop, top);
+        }
+
+        if ( (bottom < yRight) &&
+             (top > yRight) )  {
+            p2 = Base::Vector3d(right, yRight);
+        } else if (yRight <= bottom) {
+            p2 = Base::Vector3d(xBottom, bottom);
+        } else if (yRight >= top) {
+            p2 = Base::Vector3d(xTop, top);
+        }
+    }
+    result.first = p1;
+    result.second = p2;
+    Base::Vector3d dirCheck = p2 - p1;
+    dirCheck.Normalize();
+    if (!dir.IsEqual(dirCheck, 0.00001)) {
+        result.first = p2;
+        result.second = p1;
+    }
+
+    return result;
+}
+
 Base::Vector3d DrawUtil::vertex2Vector(const TopoDS_Vertex& v)
 {
     gp_Pnt gp  = BRep_Tool::Pnt(v);

src/Mod/TechDraw/App/DrawUtil.h

@@ -79,6 +79,10 @@ class TechDrawExport DrawUtil {
         static bool isFirstVert(TopoDS_Edge e, TopoDS_Vertex v, double tolerance = VERTEXTOLERANCE);
         static bool isLastVert(TopoDS_Edge e, TopoDS_Vertex v, double tolerance = VERTEXTOLERANCE);
         static bool fpCompare(const double& d1, const double& d2, double tolerance = FLT_EPSILON);
+        static std::pair<Base::Vector3d, Base::Vector3d> boxIntersect2d(Base::Vector3d point,
+                                                                        Base::Vector3d dir,
+                                                                        double xRange,
+                                                                        double yRange) ;
         static Base::Vector3d vertex2Vector(const TopoDS_Vertex& v);
         static std::string formatVector(const Base::Vector3d& v);
         static std::string formatVector(const gp_Dir& v);

src/Mod/TechDraw/App/DrawViewSection.cpp

@@ -677,6 +677,38 @@ TopoDS_Face DrawViewSection::projectFace(const TopoDS_Shape &face,
     return projectedFace;
 }
 
+
+//calculate the ends of the section line in BaseView's coords
+std::pair<Base::Vector3d, Base::Vector3d> DrawViewSection::sectionLineEnds(void)
+{
+    std::pair<Base::Vector3d, Base::Vector3d> result;
+
+    auto sNorm  = SectionNormal.getValue();
+    double angle = M_PI / 2.0;
+    auto axis   = getBaseDVP()->Direction.getValue();
+    Base::Vector3d stdOrg(0.0, 0.0, 0.0);
+    Base::Vector3d sLineDir = DrawUtil::vecRotate(sNorm, angle, axis, stdOrg);
+    sLineDir.Normalize();
+    Base::Vector3d sLineDir2 = - axis.Cross(sNorm);
+    sLineDir2.Normalize();
+    Base::Vector3d sLineOnBase = getBaseDVP()->projectPoint(sLineDir2);
+    sLineOnBase.Normalize();
+
+    auto sOrigin = SectionOrigin.getValue();
+    Base::Vector3d adjSectionOrg = sOrigin - getBaseDVP()->getOriginalCentroid();
+    Base::Vector3d sOrgOnBase = getBaseDVP()->projectPoint(adjSectionOrg);
+    sOrgOnBase /= getScale();
+
+    auto bbx = getBaseDVP()->getBoundingBox();
+    double xRange = bbx.MaxX - bbx.MinX;
+    xRange /= getScale();
+    double yRange = bbx.MaxY - bbx.MinY;
+    yRange /= getScale();
+    result = DrawUtil::boxIntersect2d(sOrgOnBase, sLineOnBase, xRange, yRange);
+
+    return result;
+}
+
 //this should really be in BoundBox.h
 //!check if point is in box or on boundary of box
 //!compare to isInBox which doesn't allow on boundary

src/Mod/TechDraw/App/DrawViewSection.h

@@ -119,6 +119,8 @@ public:
     static const char* SectionDirEnums[];
     static const char* CutSurfaceEnums[];
 
+    std::pair<Base::Vector3d, Base::Vector3d> sectionLineEnds(void);
+
 protected:
     TopoDS_Compound sectionFaces;
     std::vector<TopoDS_Wire> sectionFaceWires;